input_algorithms python import validator and normaliser

import.py

class Import(valid_string_spec):
    validators = [regexed("^(?P<module>[a-zA-Z_][a-zA-Z_0-9]*(\.[a-zA-Z_][a-zA-Z_0-9]*)*):(?P<class>[a-zA-Z_][a-zA-Z_0-9]*)$")]
    def setup(self, checked_class):
        self.checked_class = checked_class

    def normalise_filled(self, meta, val):
        # Run string & regex validator
        val = super(Import, self).normalise_filled(meta, val)

        # Now validate it is importable
        path = self.validators[0].regexes[0][1].match(val).groupdict()
        try:
            module = import_module(path['module'])
            val = getattr(module, path['class'])
            if not issubclass(val, self.checked_class):
                raise BadSpecValue(
                    "Wrong class type. {} is not a {}".format(
                          val.__name__
                        , self.checked_class.__name__
                    ),
                    meta=meta
                )
            return val
        except ImportError:
            raise BadSpecValue("Import not found", val=val, meta=meta)
        except AttributeError:
            raise BadSpecValue("Couldnt find class", val=val, meta=meta)